1. Field of the Invention
The invention relates to a method for recognizing time-variable functional states in RFID systems with at least one transponder or remote sensor and at least one base station, which transmits data and/or power to the transponder or sensor by a carrier signal. Furthermore, the invention relates to a device on a transponder or remote sensor for time-variable, process-dependent control of a data transmission in RFID or remote sensor systems with at least one base station and at least one such transponder or sensor.
2. Description of the Background Art
In recent years, automatic identification methods, also called auto-ID, have been widely used in many service sectors, in acquisition and distribution logistics, in commerce, in production, and in material flow systems. The goal of auto-ID is the extensive provision of information on persons, animals, objects, and products.
An example of such auto-ID systems are the chip cards, commonly used today, in which a silicon memory chip by mechanical-galvanic contacting is provided with power, read out, and optionally also reprogrammed by a reader, the so-called base station. In this case, the acquisition device is routinely called the reader, regardless of whether it can only read or rewrite data.
RFID systems include two basic components, namely, the transponder or sensor in the case of a remote sensor system, i.e., an application-specific integrated circuit (IC) with a coupling element, such as a dipole antenna as the transmitting and receiving device, and the base station, which typically has a high-frequency module (transmitter-receiver) and a coupling element. Data are transmitted both from the base station to the transponder or sensor (forward link) and in the opposite direction (return link).
In RFID systems, the data carrier, the transponder or sensor, can be supplied with power not only through galvanic contacting but also contactless with use of electromagnetic fields within the radio frequency (RF). Transponders or sensors without any independent energy source are called “passive” transponders or sensors. Those with an (additional) independent energy supply, e.g., by a battery, are called “semi-passive” transponders or sensors.
Such RFID systems, whose range is considerably greater than 1 m, work with electromagnetic waves in the UHF and microwave range. In this case, a backscattering method, called the backscatter principle because of its physical operating mode, is used predominantly during the course of which a portion of the energy arriving at the transponder or sensor from the base station is reflected (backscattered; so-called backscattering) and in so doing is optionally modulated for data transmission: The IC receives via the coupling element a high-frequency carrier, designated hereafter also as the carrier signal, which it transmits by suitable modulation and backscattering devices partially back to the base station.
The transponders and sensors, named above as components of such a system, are also typically, as well as generalized hereafter, called tags.
For certain applications, the aforementioned tags have a writable memory, such as an EEPROM or the like, and are accordingly programmable by a suitable command from the base station. In this regard, in RFID applications, particularly during use of purely passive tags, it occurs routinely during programming that to achieve increased programming ranges for the purpose of assuring a sufficient power supply for an appropriate process duration, the allocated programming time (duration) must be lengthened. An appropriately designed RFID system must then reserve sufficient derivative time in the control case, which disadvantageously leads to lengthening of the communication. Furthermore, the programming time can be different also when different memory technologies are used. Furthermore, it can occur in sensor applications that a measured value is available only after a certain, variable time.
“Processes” will also be used as a general term hereafter instead of sequences of operations such as programming, a reading process, a measurement, or the like. A process state thereby is understood to be a quantitative and/or qualitative progression of the process, e.g., its ending, particularly in conjunction with an evaluation of the process result, such as “successfully completed” or “not successfully completed.”
A prior-art approach to avoid the aforementioned disadvantage is the use of so-called autoincrement or autodecrement techniques. In this case, after completion of a process, such as programming, for example, by a short command (shortened compared with the process command), an additional data stream is transmitted from the base station to the tag, which is then immediately programmed, without an associated (memory) address being transmitted, because it was automatically changed (by autoincrement/autodecrement). Alternatively, the same datum is programmed in the next address (also by a suitable short command). In this case, it is to be regarded as particularly disadvantageous that after completion of such a process sequence, the entire memory must be read out to assure that all data were saved, which in turn represents a considerable additional time expenditure. Moreover, a transmission is then no longer possible in regard to quality of the programming (dwell time, data retention time).
In the Palomar protocol (cf. ISO submission ISO/IEC 18000-6 WD Mode3 of 1 Feb. 2002), information on the quality of the programming is transmitted in a status word after a programming process. This technique, however, disadvantageously requires that this status word is requested also in fact after completion of the programming.
The German patent application DE 103 56 259, which corresponds to U.S. Publication No. 20050122651, which is herein incorporated by reference, discloses a method by which a tag automatically adjusts the programming time to the conditions of the field or to a power source supplying it.
DE 101 38 217 A1, which corresponds to U.S. Publication No. 20030133435, which is herein incorporated by reference, relates to a method in which to transmit data by a header section in the data protocol, by which a number of symbols used for coding in the data field and their identification are defined, the data rate is adjusted to the communication conditions. In this case, the data rate can be substantially increased by reducing, for example, the number of symbols and/or simplifying their identification at a large communication distance.
Furthermore, it is known in conventional programming applications to again provide data for control after their programming. In this case, it is to be regarded as particularly disadvantageous that whether the data are now present can hardly be verified in this way; information on the retention time cannot be derived, however.
Another obvious solution to the aforementioned problem is to search for a load change signature in the “transmit signal” of the tag: If a purely passive tag is used, a load change affects the aforementioned transmit signal (backscatter signal) of the tag behind its routinely present rectifying means to generate a supply DC voltage from the alternating field power transmitted by the base station. After this change, the base station can search by observing its incoming signal. In this case, however, it is to be regarded as particularly disadvantageous that, on the one hand, in a noisy environment a single load change is not received reliably and that, on the other, in semi-passive tags a load change does not affect the backscatter, because the power supply of the tag does not come from the field by definition. For this reason, this type of detection cannot be used particularly in mixed systems, i.e., systems supporting both passive and semi-passive tags.
If, moreover, a time-variable process is integrated into the system, e.g., computational determination of a certain parameter, measurement of a physical parameter in the sensor applications, or the like, which routinely only has little effect on load behavior and thus on backscatter, recognition of the process state is also not possible in the manner described above.
GB 2 308 947 A, GB 2 390 508 A, U.S. Pat. Nos. 6,720,866 B1, and 6,712,276 B1 are directed to methods and devices, whereby sensor data is transmitted from a transponder to a base station.